This invention relates to a radio paging receiver for receiving a pager signal comprising a call number signal and a message signal.
A recent remarkable development of an integrated circuit technique has rendered the radio paging receiver compact or portable and multifunctional. Preferably, the radio paging receiver has a long life. Inasmuch as a battery is used as a power source in the radio paging receiver, the radio paging receiver has a life time dependent upon the life of battery. Therefore, electric power must not be wasted in the radio paging receiver. In other words, useless operation should strictly be restricted. For this purpose, a battery saving operation is carried out in such a radio paging receiver.
As an example of the radio paging receiver, a synchronous type is well known in the art. In the synchronous type, the radio paging receiver receives a pager signal comprising a succession of frames each of which has a frame period Ft and which consists of first through n-th group signals where n represents a positive integer greater than unity. Each of the first through the n-th group signals has a signal duration Dt and comprises a call number signal representative of a call number and a message signal representative of a message.
As known in the art, the radio paging receiver has a preassigned call number which belongs to one of the first through the n-th group signal. The radio paging receiver comprises a receiving section for receiving the pager signal, a battery saving switch connected between a battery and the receiving section, and a control unit for controlling said battery saving switch. The battery saving switch has on and off states and supplies electric power to said receiving section in the on state. The control unit puts the battery saving switch into the on state so that the receiving section receives only the one of the first through the n-th group signals to which the preassigned call number belongs. In other words, the receiving section periodically carries out a receiving operation at the frame period Ft and receives the one of the first through the n-th group signals as a reception group signal. This means that the battery saving operation is carried out in the radio paging receiver. Thus, the control unit serves as a switch driving unit for carrying out the battery saving operation.
The receiving section supplies the reception group signal to the control unit. The control unit carries out a decision operation whether or not the reception group signal contains the call number signal representative of the call number which is coincident with the preassigned call number. Namely, the control unit also serves as a decision unit for carrying out the decision operation. If the reception group signal contains the call number which is coincident with the preassigned call number, the control unit further carries out a decoding operation of the message signal to obtain the message represented by the message signal. As a result of the decoding operation, the control unit energizes a speaker or drives a display unit in order to display the message. Such a radio paging receiver is disclosed in Japanese Unexamined Patent Publication Tokkai Hei 2-5633, namely, 5633/1990 and is suitable for receiving the pager signal having a data transmission rate of 1200 (bps) at most.
In the meanwhile, it is required that the decoding operation is carried out in high speed as the data transmission rate is increased. In this event, the control unit requires a clock signal having a high clock rate in order to establish a frame synchronization. Under the circumstances, the radio paging receiver further comprises first and second clock signal generating circuits which are for generating first and second clock signals, respectively. The first clock signal has a first clock rate while the second clock signal has a second clock rate higher than the first clock rate. The control unit operates in synchronism with the first clock signal while the control unit puts the battery saving switch into the off state. The control unit carries out the decision operation in synchronism with the first clock signal. If the control unit decides that the reception group signal contains the call number which is coincident with the preassigned call number, the control unit carries out the decoding operation in synchronism with the second clock signal. When the control unit operates in high speed, the control unit increases in power consumption. This means that the radio paging receiver has a degraded battery saving effect. In addition to the degraded battery saving effect, it is hard to establish a frame synchronization as the data transmission rate is increased.